Pavan K. Aluri

Parity asymmetry in the CMBR temperature power spectrum

We study the power asymmetry between even and odd multipoles in the multipolar expansion of cosmic microwave background temperature data from the Wilkinson Microwave Anisotropy Probe (WMAP), recently reported in the literature. We introduce an alternate statistic which probes this effect more sensitively. We find that the data are highly anomalous and consistently outside the 2σ significance level in the whole multipole range l = [2, 101]. We examine the possibility that this asymmetry may be caused by the foreground cleaning procedure or by residual foregrounds. By direct simulations we rule out this possibility. We also examine several possible subdominant foregrounds, which might lead to such an asymmetry. However, in all cases we are unable to explain the signal seen in data. We next examine cleaned maps, using procedures other than that followed by the WMAP science team. In particular, we analysed the maps cleaned by the Internal Powar Spectrum Estimation (IPSE), needlets and the harmonic Internal Linear Combination (ILC) procedures. In all these cases, we also find a statistically significant signal of power asymmetry if the power spectrum is estimated from the masked sky. However, the significance level is found to be not as high as that in the case of the WMAP best-fitting power spectrum. Finally, we test the contribution of low-l multipoles to the observed power asymmetry. We find that if we eliminate the first six multipoles, l = [2, 7], the significance falls below the 2σ confidence level. Hence, we find that the signal gets dominant contribution from low-l modes.

LARGE SCALE ANISOTROPY DUE TO PRE-INFLATIONARY PHASE OF COSMIC EVOLUTION

We show that perturbations generated during the anisotropic pre-inflationary stage of cosmic evolution may affect cosmological observations today for a certain range of parameters. Due to the anisotropic nature of the universe during such early times, it might explain some of the observed signals of large scale anisotropy. In particular, we argue that the alignment of CMB quadrupole and octopole may be explained by the Sachs–Wolfe effect due to the large scale anisotropic modes from very early times of cosmological evolution. We also comment on how the observed dipole modulation of CMB power may be explained within this framework.

DARK ENERGY AND DARK MATTER IN GENERAL RELATIVITY WITH LOCAL SCALE INVARIANCE

We consider a generalization of Einsteins general theory of relativity such that it respects local scale invariance. This requires the introduction of a scalar and a vector field in the action. We show that the theory naturally displays both dark energy and dark matter. We solve the resulting equations of motion assuming an FRW metric. The solutions are found to be almost identical to those corresponding to the standard ΛCDM model.

Direction dependence of cosmological parameters due to cosmic hemispherical asymmetry

Persistent evidence for a cosmic hemispherical asymmetry in the temperature field of cosmic microwave background (CMB) as observed by both WMAP as well as PLANCK increases the possibility of its cosmological origin. Presence of this signal may lead to different values for the standard model cosmological parameters in different directions, and that can have significant implications for other studies where they are used. We investigate the effect of this cosmic hemispherical asymmetry on cosmological parameters using non-isotropic Gaussian random simulations injected with both scale dependent and scale independent modulation strengths. Our analysis shows that As and ns are the most susceptible parameters to acquire position dependence across the sky for the kind of isotropy breaking phenomena under study. As expected, we find maximum variation arises for the case of scale independent modulation of CMB anisotropies. We find that scale dependent modulation profile as seen in PLANCK data could lead to only 1.25σ deviation in As in comparison to its estimate from isotropic CMB sky.

Relating the inhomogeneous power spectrum to the CMB hemispherical anisotropy

We relate the observed hemispherical anisotropy in the cosmic microwave radiation data to an inhomogeneous power spectrum model. The hemispherical anisotropy can be parameterized in terms of the dipole modulation model. This model leads to correlations between spherical harmonic coefficients corresponding to multipoles, l and l+1. We extract the

Effect of Foregrounds on the CMBR Multipole Alignment

l

Effect of foregrounds on the cosmic microwave background radiation multipole alignment

dependence of the dipole modulation amplitude, A, by making a fit to the WMAP and PLANCK CMBR data. We propose an inhomogeneous power spectrum model and show that it also leads to correlations between multipoles, l and l+1. The model parameters are determined by making a fit to the data. The spectral index of the inhomogeneous power spectrum is found to be consistent with zero.

CONSTRAINTS ON THE COSMOLOGICAL CONSTANT DUE TO SCALE INVARIANCE

We analyze the effect of foregrounds on the observed alignment of CMBR quadrupole and octopole. The alignment between these multipoles is studied by using a symmetry based approach which assigns a principal eigenvector (PEV) or an axis with each multipole. We determine the significance of alignment between these multipoles by using the Internal Linear Combination (ILC) 5 and 7 year map s and also the maps obtained by using the Internal Power Spectrum Estimation (IPSE) procedure. The effect of foreground cleaning is studied in detail within the framework of the IPSE method both analytically and numerically. By using simulated CMBR data, we study how the PEVs of the pure simulated CMB map differ from those of the final cleaned map. We find that, in general, the shift in the PEVs is relatively small and in random directions. Due to the random nature of the shift we conclude that it can only lead to misalignment rather than alignment of multipoles. We also directly estimate the significance of alignment by using simulated cleaned maps. We find that the results in this case are identical to those obtained by simple analytic estimate or by using simulated pure CMB maps.

Alignments of parity even/odd-only multipoles in CMB

We analyze the effect of foregrounds on the observed alignment of CMBR quadrupole and octopole. The alignment between these multipoles is studied by using a symmetry based approach which assigns a principal eigenvector (PEV) or an axis with each multipole. We determine the significance of alignment between these multipoles by using the Internal Linear Combination (ILC) 5 and 7 year map s and also the maps obtained by using the Internal Power Spectrum Estimation (IPSE) procedure. The effect of foreground cleaning is studied in detail within the framework of the IPSE method both analytically and numerically. By using simulated CMBR data, we study how the PEVs of the pure simulated CMB map differ from those of the final cleaned map. We find that, in general, the shift in the PEVs is relatively small and in random directions. Due to the random nature of the shift we conclude that it can only lead to misalignment rather than alignment of multipoles. We also directly estimate the significance of alignment by using simulated cleaned maps. We find that the results in this case are identical to those obtained by simple analytic estimate or by using simulated pure CMB maps.

Novel approach to reconstructing signals of isotropy violation from a masked CMB sky

We consider the standard model with local scale invariance. The theory shows exact scale invariance of dimensionally regulated action. We show that massless gauge fields, which may be Abelian or non-Abelian, lead to vanishing contribution to the cosmological constant in this theory. This result follows in the quantum theory, to all orders in the gauge couplings. However, we have not considered contributions higher orders in the gravitational coupling. Similarly we also find that massless fermion fields yield null contribution to the cosmological constant. The effective cosmological constant in this theory is nonzero due to the phenomenon of cosmological symmetry breaking, which also gives masses to all the massive fields, besides generating the Planck mass. We find a simple relationship between the curvature scalar and the vacuum value of the Higgs field in the limit when we ignore all other contributions to the energy density besides the vacuum energy.